ensure `monolengthbonus` applies to new strain contribution only

[Lawtrohux]

The aim of this PR is correct the application of monoLengthBonus within Stamina.

Mainly, the bonus was applied to the accumulated strain, rather than new strain contribution, causing issues on some maps where removing objects can increase SR due to applying the bonus already decayed notes. This effect was not intended, and whilst isn't a huge issue, should see some difficult mono maps rightfully getting a buff, as well as fixing something actually broken.

Similarly, it disables it inside of singlecolourstamina, in which it would skew values that are displaying for mainly convert-esque maps. This also means that convert values should now display correctly true to their intended values.

[Lawtrohux]

@ppy/pp-maintainers could i grab a smoogisheet for this please? preferably one with converts-only and without. Thank you!

[stanriders]

!diffcalc RULESET=taiko OSU_A=https://github.com/ppy/osu/tree/pp-dev OSU_B=https://github.com/ppy/osu/pull/33635

[github-actions[bot]]

Difficulty calculation failed: https://github.com/ppy/osu/actions/runs/15765452591

[stanriders]

!diffcalc RULESET=taiko OSU_A=https://github.com/ppy/osu/tree/pp-dev OSU_B=https://github.com/ppy/osu/pull/33635

[github-actions[bot]]

Target: https://github.com/ppy/osu/pull/33635 Spreadsheet: https://docs.google.com/spreadsheets/d/19xWuwLERTO-Q8UPaSXoqqI46GzxOPGGDIULtJtAshRc/edit

[buyaspacecube]

looks like it!